This invention relates to a device for measuring a flow property of granular materials and more particularly relates to a device for measuring the angle of repose of granular material in both the static and dynamic modes.
The flow properties of dry particulate or granular materials have long been of interest to many different fields of science. Such diverse fields of endeavor as the food industry, as well as the fuel and mining industry are interested in the flow properties of dry granular material. In additon the science of xerography is concerned with the flow of dry particulate material as such materials are employed as the writing or marking materials employed in the modern science of "dry writing". One of the well known measurements employed to provide an indication of the flow characteristics of granular material is called the angle of repose which is determined by allowing the granular material to fall into a pile on a horizontal surface from a predetermined and known distance. The shape of the pile is determined by measuring the angle formed by the outer surface of the pile with the horizontal surface upon which the material rests. This measurement is commonly termed the "dynamic" angle of repose. The device normally employed for such measurements is simply a funnel held a certain distance above a horizontal surface.
The "static" angle of repose is also measured by such simple devices as a rectangular container having an orifice in its center to permit the escape of the granular material from the bottom center of the container leaving a cavity in the volume of material remaining in the container. The slope of this angle with the horizontal is termed the static angle of repose. While the several devices of the prior art are simple in construction their use is not without difficulty because of experimental error easily produced. In addition, the material being measured is employed repeatedly in successive tests in order to provide an average figure reducing the effects of experimental error. Accordingly, a more accurate and convenient means is needed for the measurement of flow properties of granular material particularly as indicated by its angle of repose.